1. Field of the Invention
This invention relates to a coating solution for forming a selectively transmitting film on a transparent base, such as glass or plastics. More particularly, it relates to a selectively transmitting film, or multilayer film for transmitting, reflecting or absorbing ultraviolet radiation, heat rays, visible light or infrared radiation selectively depending on the purpose for which it is used, and a coating solution for forming the same.
2. Description of the Prior Art
Ultraviolet radiation is feared, since it has been showing a sharp increase in its amount reaching the Earth as a result of the formation, or enlargement of holes in the ozone layer, and has an adverse effect on the human body by, for example, causing sunburn, or a cancer of the skin. It passes through windows into houses, buildings, automobiles, shops, etc., and causes the fading, discoloration, or deterioration of curtains, carpets, sofas, or other pieces of furniture, pictures, papers, etc.
Oxides of titanium, cerium or zinc have, for example, been known as an agent for cutting off ultraviolet radiation, but as they have a low absorbance of ultraviolet radiation having long wavelengths in the vicinity of 400 nm, none of these compounds has been satisfactory as a material for cutting off wavelengths in the vicinity of 400 nm if they are used alone.
Another known agent for cutting off ultraviolet radiation comprises an organic compound such as benzophenone. It has a high absorbance of ultraviolet radiation, but it has been difficult to expect from it a steady power of cutting off ultraviolet radiation for a long time, since it is decomposed by absorbing ultraviolet radiation.
Attention has recently come to be drawn to glass for cutting off heat rays for saving the consumption of energy by cutting off the entry of the heat energy of sunlight through windows and thereby reducing the load of air conditioners during summer, and glass having a regulated transmittance of visible light for the protection of privacy. These sheets of glass have, however, had a demand differing widely in the place of use, color, transmittance of light, and the power of cutting off heat rays, and as the functional films formed on those sheets of glass for imparting the necessary functions to them have mostly been formed by a dry process such as sputtering, or vapor deposition, it has been difficult to manufacture many kinds of different products each in a small quantity to satisfy any and all demands, and the necessity for large equipment and complicated operation has meant a very high cost of manufacture. Moreover, there have been available few products having a power of cutting off ultraviolet radiation having wavelengths particularly in the vicinity of 400 nm, nor has there been substantially any glass adapted to control the transmission of all of ultraviolet radiation, heat rays (solar energy) and visible light.
A film colored with an organic dye has also been commercially available, but no such film has been very effective, as the dye is seriously damaged by ultraviolet radiation, etc.
The dry process used for forming the functional films as stated above requires large and complicated vacuum equipment, etc., and has been inapplicable to any work that has to be done on any glass in, say, the windows of existing houses, buildings, automobiles, etc.